Somewhere in the north-eastern Spanish city of Borja, an elderly woman is probably praying that the road to hell is not really paved with good intentions.

There can be little doubt that the woman, identified only as an octogenarian local, was just trying to help when she noticed that the face of the scourged Christ on the wall of a small church in the city was looking a bit faded, and decided to freshen it up a bit.

Sadly for her – and Elías García Martínez, the 19th-century artist who painted the mural – her brush skills were not quite up to the job.

The unnamed amateur has transformed what was once a pleasant, if unremarkable, Ecce Homo into something that more closely resembles a bloated hedgehog than the image of Jesus before Pilate.

The press have dubbed her efforts "the worst restoration in history" and "a botched job", and the Borja authorities fear they are right.

According to the local paper, El Heraldo de Aragón, the damage inflicted on the mural in the church of the Santuario de la Misericordia is being investigated by experts, but the artist's descendants are said to be unhappy that an individual decided to take the restoration job into her own hands and fear her handiwork is irreversible.

Juan María de Ojeda, a city councillor, said the woman, acting "spontaneously and with good intentions", had confessed what had happened as soon as she realised "that things had got out of hand".

He added that while the mural was not a work of great importance, it retained a certain sentimental value as the artist's family still have strong links to the area.

"The family used to come here on holiday," Ojeda told El País. "He painted the picture one summer and left it to the town."

The centre posted some graphic before-and-after pictures, along with a plaintive message confirming that someone had recently been up to no good with a brush.

"As incredible as it may seem, this is all that remains of the work of an artist whose descendants still live in our city," it said. "We do not know whether this unspeakable deed can de remedied, but there can be no doubt whatsoever that someone should take the necessary action to ensure that such behaviour is not repeated. Whatever the motives were, it must be roundly condemned."